As shown in FIG. 1, a prior art wheelchair 1 comprises mainly a seat frame 10 to which two casters 11 and two wheels 12 are fastened pivotally. The wheelchair 1 can be caused to move by driving the two wheels 12 with hands of a person sitting on the wheelchair 1. In addition, the seat frame 10 of the wheelchair 1 is provided respectively at the top ends of the left side and the right side of the rear portion thereof with a hand grip to facilitate the pushing of the wheelchair 1 by a person standing behind the wheelchair 1.
Such a prior art wheelchair as described above has inherent shortcomings, which are expounded explicitly hereinafter.
It is conceivably difficult and tiresome for a person, who is unable to walk and confined to the wheelchair 1 of the prior art, to drive the two wheels 12 so as to keep the wheelchair 1 on the move. Needless to say, the person can become severely strained if he or she drives the two wheels 12 with his or her hands so as to keep the wheelchair 1 moving at a speed as fast as 1.39 m/s, which is an average of the maximum effective speeds of the conventional manually-operated wheelchairs.
The action of driving the two wheels 12 of the prior art wheelchair 1 with both hands of a person who is confined to the wheelchair 1 can inflict a shoulder or elbow injury on the person.
The prior art wheelchair 1 is not provided with a braking means. As a result, the wheelchair 1 on the move must be stopped manually with both hands of a person who is confined to the wheelchair 1. Both hands and wrists of the person are therefore rather vulnerable to injury.
The prior art wheelchair 1 is in fact hazardous to the safety of a person who is confined thereto. The casters 11 and the wheels 12 of the wheelchair 1 are substantially different in size from each other. The wheelchair 1 is therefore highly vulnerable to accident, especially when the wheelchair 1 is driven on a bumpy surface.
With a view to overcoming some of the foregoing shortcomings of the prior art wheelchair 1, an improved wheelchair was disclosed in the U.S. Pat. No. 4,762,332. The improved wheelchair is provided with a transmission mechanism and an operating lever by which a person, who is confined to the wheelchair, can drive the wheelchair.
Such an improved wheelchair as disclosed in the U.S. Pat. No. 4,762,332 is inherently defective in design in that the operating lever is operative only in a one-way manner, and that the transmission mechanism is rather complicated in construction, and further that the improved wheelchair which is also provided with two casters and two large wheels is unsafe to ride on a surface in general and a bumpy surface in particular.